This invention relates to an improvement of a multi-layered hollow coil of a self-melting wire, and an apparatus and method of manufacturing thereof of the Japanese patent Application Nos. 208299/81 (the application laid open No. 108937/83) and 187148/84 assigned to the assignee and more particularly to a hollow coil having multi-layered windings for use in a rotatable electric equipment having no iron core, and an apparatus and method of manufacturing the coil by two winding operations due to a reversible coil matrix.
In past, U.S. Pat. No. 4,355,459 to Teruo Takahashi et al and UK Patent No. 2048137 B disclose an apparatus and method of coiling a wire in a rotatable tube. And, in the above stated Japanese patent application laid open No. 108937/83, a multi-layered hollow coil and a method of manufacturing thereof are disclosed, in which a wire is wound on a core disposed between spool-type flanges to place both first and last ends of the first layer in opposite portions adjacent to the flanges and to wind second layer between respective crests of the windings of the first layer, and the layers are repeated to place the layers in odd numbers on the same situation of the first layer and to place the layers in even numbers on the same situation of the second layer.
Generally, it is desired that a multi-layered hollow coil for use in a rotatable electric equipment having no iron core, be as small as possible. And, it is necessary to electrically insulate a wire and to wind the wire in order to effectively use the space and achieve a predetermined thickness of the coil. For this purpose, it is required that gaps or spaces do not occur in the coil during the winding of multi-layers.
A conventional winding method of a multi-layered hollow coil utilizes a core for the coil, a center of which has the same shape as an inner shape of the hollow coil. The core has a width which corresponds to a predetermined width of the coil between flanges which are fixed to both sides of the core. One of the flanges may be slidably mounted on the core. A wire is wound in the space of the coil width on the core to provide multi-layers from a first layer in order. In any core, in order to wind the wire on the core having fixed flanges, the first layer of the wire is wound from a corner between an inner face of one of the flanges and an axle portion of the core in accordance with a fixed pitch through a wire guide, and when a last winding of the first layer reaches the other flange at the other side, a second or next layer layer is wound. At this time, when the wire is wound a corresponding number of times (a predetermined number) as the first layer, the wire of the second layer is spirally wound between the crests of the wire of the first layer with a reversed direction pitch as compared to the first layer. If the wire of the first layer reaches the opposite flange prior to completing the predetermined number of windings, namely, if the wire of the first layer is wound at broader intervals than the predetermined regular intervals, a wire guide is not reversed because the wire has not completed winding the predetermined number, and a first wire portion of the second layer is wound one above the other on the crest of the last winding of the first layer because the wire of the second layer is prevented or blocked by the flange. Subsequently, after completion of the predetermined number of windings, the wire guide changes its pitch to a winding start portion of a next winding direction. Occasionally this stage, the wire in the second layer is not precisely wound between the crests of the first layer, and the wire for the second layer jumps over the crest adjacent to the last two crests and starts winding of the second layer on the next crest to turn back to the first portion of the first layer.
The portion which the wire jumped over in the second layer will be the cause of a further jumping in windings of a third and continuous layers and many gaps occur at the jumping portions in a coil, therefore, the space of the thickness of the coil is not effectively used, and the shape of the coil eventually becomes uneven.
From our experience, it is found that when the first winding portion of the first layer at a flange and the last winding portion of the first layer at the other flange, after winding a predetermined number times and which corresponds to a portion of the wire that is moved to the second layer, are placed at corresponding opposite places proximate the inner walls of the flanges and when the winding is shifted to the second layer, the shifted wire is exactly wound between the crests of the windings of the first layer. And, when the winding of the second layer is shifted to a third layer, the wire is exactly wound between the crests of the windings of the second layer, and the subsequent layers after a fourth layer are exactly wound between the crests of the windings of a lower layer.
But, an insulated wire having an uneven cross section (due to) an accidental error in formation of the diameter thereof), after being wound a predetermined number of turns to achieve a predetermined thickness for the coil, does not have a first winding portion of the first layer correspond to the last end winding portion of the first layer such that the end portions are not always positioned at the opposite portions of the inner walls of the flanges since both end flanges are fixed at a predetermined thickness or width of the coil.
Therefore, excess windings of the wire is heaped up on the last winding of the first layer, because the winding of the first layer does not achieve the predetermined number turns and the excess winding of the wire shifts to the second layer. Accordingly, a wire guide changes its pitch to start winding the wire to an opposite direction after the predetermined number of windings for the first layer, but the wire of the second layer is not placed between the crests of the wire of the first layer, and the wire jumps the next crest or crests and is inadvertently wound between unexpected crests of the lower layer and is wound to the first winding direction of the lower layer. For reasons, a wire guide guides the wire on a core of the coil in accordance with a predetermined pitch and the wire guide does not change the direction of the pitch, as compared to the first winding direction of the presently wound layer, until a predetermined number of windings are placed on the core even though the last winding of the first layer reaches the inner wall of the opposite flange along the thickness (width) of the coil between both flanges of the core, and the next winding is heaped up the first layer adjacent the fixed flange, and the predetermined number of wire windings is not able to be accommodated in the space which corresponds to the expected thickness of the coil. Under these circumstances, it is difficult to wind a wire with multi-layers between the crests of windings in manufacturing a coil of the multi-layers of the wire which do not have an even cross section and an uniform diameter such as a fusion wire.
Therefore, in a conventional winding method and apparatus for manufacturing a multi-layer hollow coil, first and second layers are wound on a core of coil which has flanges at both ends through a flier. And, after winding the second layer, once the winding through the flier is stopped and the core is reversely rotated against the direction of rotation of the flier during stopping the flier, and a wire extended to an opposite side of the flier is wound on the core adjacent the first and second layers and subsequently the wire is wound to upper layers in order. But, in the conventional method and apparatus, the strain of one twist of the wire occurs per one rotation of the flier, because the wire is wound due to rotation around the core by the flier. And, during winding the wire on the core of the coil, it is difficult to correctly spirally wind the wire on the lower layer due to the strain caused on the wire with twist of each rotation. Therefore, jumped windings easily occur in the conventional multi-layers and accordingly there is a disadvantage that the balanced torque occurred on a rotatable electric machine is not expected.
Further, in a conventional method, a wire, which is appropriately extended, is wound from the extended portion a predetermined number at a first side, and after winding the first layer at the first side the wire is shifted for a second layer at the first side and a flier is displaced to the opposite direction of the lower layer to wind the second layer. After winding the second layer, the rotation of the flier is once stopped and the core is reversely rotated against rotation of the flier due to the wire which is extended to other direction at the first winding portion of the first layer. After winding the first and second layers at a second side, the rotation of the core is stopped. Subsequently, again the flier is rotated and the third and fourth layers at the first side are wounded. And again the flier is stopped and the core is reversely rotated against the flier and the third and fourth layers at the second side are wound. In the same manner, continuous layers at the first and second sides are alternatively wound. Therefore, there are many stops for the winding machine during winding processes in the conventional method. Accordingly, it is obliged to provide and combine mechanisms for reducing the speed and for stopping the machine, and it is difficult to increase number of rotations of the core due to continuous operation of the respective steps of winding the wire, and it is difficult to efficiently operate the steps.
In the above-stated conventional method, turnings of the layer of the multi-layers are based on the adjacent wall portion of the wound wire and moves to higher layer, and the windings are reciprocally turned to the opposite directions upon the lower layer, because both flanges of the core are fixed or a slidable flange of the core is fixed during winding the wire. Therefore, each winding of the each layer is not correctly placed between the crests of the windings of the lower layer and is jumped. Accordingly, gaps in the coil occur and the ratio in windings of the wire in the predetermined width of the coil falls.